This invention resides in a method of controlling a heating device for the regeneration of a particle filter arranged in the exhaust duct of an internal combustion engine such as a Diesel engine, wherein the exhaust gas back pressure caused by the particle filter is determined as an indication for the soot charge state of the particle filter.
For the reduction of the emission of particles, particularly the emission of soot during operation of Diesel engines, so-called Diesel particle filters are installed in the exhaust duct of the Diesel engine such that the exhaust gas is conducted through the filter body of these particle filters. During this process, particles contained in the exhaust gas are deposited on the upstream surface of the filter body, particularly soot particles. Starting with a new particle filter without any soot deposits increasing amounts of soot are deposited on the upstream surface of the filter body over a period of operation. In order to ensure that the sufficient exhaust gas can flow through the filter over an extended period, the soot removed from the exhaust gas and deposited on the particle filter must be removed from time to time. The removal of the soot from the particle filter is also called regeneration of the filter.
For the regeneration of such a particle filter the soot deposited on the filter is burnt off. The removal of this soot deposited on the upstream filter surface occurs automatically when the temperature of the exhaust gas reaching the surface of the particle filter is higher than the ignition temperature of the soot. In a Diesel engine, this is the case if it is operated over a certain time under a certain load, for example, in a passenger vehicle during high speed Autobahn travel. However, in order to ensure regeneration and consequently the intended operation of a particle filter also under engine load conditions when the exhaust gas temperature is below the ignition temperature of the soot, methods have been developed by which the particle filter can be regenerated depending on the soot charge state of the particle filter. Then the soot is burnt off by the generation of additional thermal energy for example, by thermoelectric heating elements or by a burner or an oxygen control which results in increased exhaust gas temperatures. In order to provide for a predetermined regeneration of the particle filter by burning off the soot, a certain amount of soot must have been collected on the upstream surface of the particle filter. If the amount of soot collected on the filter surface is too small, the soot may be burnt off only incompletely. And if the amount of soot collected on the filter surface is too large, the particle filter may be damaged during soot burn off.
For this reason, in a known method this exhaust gas back pressure in the exhaust duct ahead of the particle filter is determined since the exhaust gas back pressure is a measure for the charge state of the particle filter. With increasing soot charge of the particle filter the exhaust gas back pressure increases. However, the back pressure developing in this part of the exhaust gas duct is not only dependent on the charge state of the particle filter, but also on other engine operating values, for example, the engine load at the point in time when the exhaust gas back pressure is measured. In motor vehicles in which this method is used, therefore for determining the charge state of the particle filter, not only the exhaust gas back pressure is measured, but also the operating state of the engine and particularly engine load values such as the combustion air flow supplied to the engine and engine speed are taken into consideration. With these and additional values the exhaust gas pressure is evaluated for the determination of the charge state of particle filter while eliminating the fault values which are included in the exhaust gas back pressure signal but which are not usable for the determination of the charge state of the particle filter. In this regard, such a method, if used for example in connection with a motor vehicle or in connection with construction machinery powered by a Diesel engine, must include several data intersections for determining the required values and evaluating them. Even if the establishment of the intersections should not be particularly problematic in connection with a new vehicle design it is in general an exclusion criterion to install in an existing motor vehicle. A Diesel particle filter must be regenerated after certain periods of operation if this is to be done at reasonable expense. The same applies to construction machinery.
Based on the state of the art as discussed above it is the object of the present invention to provide a method of installing a heating device of a particle filter wherein the soot charge state of the filter can be sufficiently accurately determined without the need for several intersections for supplying certain engine operating condition values.